Method and apparatus for titrating liquids

ABSTRACT

Apparatus for dosing from a titrant reservoir and transferring or metering discrete quantities of the titrant to an unknown sample. An electric analog signal is generated in response to liquid transference representative of the amount of liquid transferred. Calibration circuits weight the analog signal to reflect titrant concentration and sample volume and thereby provide direct readout on a display means, such as a digital voltmeter for example, of a titrated sample concentration. The calibration circuits also furnish analog subtraction of the analog signal to establish direct readout of the concentration of a back-titrated sample.

[ 1 Jan. 30, 1973 OTHER PUBLICATIONS Kateman et al., Anal. Chem. 36, No.1, January 1964, pp. 253-254.

Primary Examiner-Morris O. Wolk Assistant ExaminerR. M. ReeseAtt0mey-George J. Netter and Kendrick and Subkow [57] ABSTRACT Apparatusfor dosing from a titran t reservoir and transferring or meteringdiscrete quantities of the titrant to an unknown sample. An electricanalog signal is generated in response to liquid transferencerepresentative of the amount of liquid transferred. Calibration circuitsweight the analog signal to reflect titrant concentration and samplevolume and thereby provide direct readout on a display means, such as adigital voltmeter for example, of a titrated sample concentration. Thecalibration circuits also furnish analog subtraction of the analogsignal to establish direct readout of the concentration of aback-titrated sample.

6 Claims, 4 Drawing Figures Springfield, SangamonGilmont......................v....73/4256 X .23/253 METHOD AND APPARATUSFOR TITRATING LIQUIDS inventor: Samuel G. Southwick, l50l Leland Avenue,County, Ill. 62704 Filed: Feb. 4, 1970 Appl. No.: 8,585

US. Int. Cl. .......B67d 5/26, GOln 1/14, GOln 31/16 Field ofSearch..............

I References Cited- UNITED STATES PATENTS 7/1960 l/I970 ChartounietUnited-States Patent Southwick PATENTEUJAH 30 I975 SHEET 1 OF 3 INVENTOR5/7/14064 6. SOVTHW/CK Afrae/vy METHOD AND APPARATUS FOR TITRA'IINGLIQUIDS The present invention relates generally to dispensing liquids,and, more particularly, to method and apparatus for titrating liquidsand automatically calculating titrimetric values.

BACKGROUND OF THE INVENTION Conventional manual titrations are difficultand tedious, requiring the addition of precise quantities of knownreagents to an unknown solution by such means as a pipette, for example,until a change in some chemical or physical property is detectedindicating completion of the titration. Determination of the unknownsolution concentration is then customarily achieved by a separatecalculation step. 1

Typically, calculation of the concentration of an unknown samplesinvolves solution of an equation similar to the following:

where,

Cs unknown sample concentration, Ct titrant concentration, Vs samplevolume, Vt titrant volume required. It is instructive to note that inany given titration the titrant concentration and sample volume are bothknown and constant. Accordingly, the ratio Ct/Vs is constant for thetitration, which fact is important to the practice of this invention aswill be described later herein.

In certain situations, titrimetric concentration determination of anunknown sample is somewhat more complex, requiring multiple titrations,which technique is commonly referred to as back-titration. That is, thesample is added to a first known or reference solution until partialequilibration is obtained, the reference solution is titrated with afurther known solution both before addition of the unknown sample, andthen the reference solution with unknown sample is titrated. Calculationof the unknown concentration is required as in the case of simpletitration.

Back-titration calculation can be accomplished by solving the followingmathematical equation:

where,

Cs unknown concentration,

Ct titrant concentration,

Vs sample volume,

reference solution alone,

Vt2 required titrant volume to equilibrate reference solution afterunknown sample added.

Again, it is important to note that Ct/Vs is constant, and therefore,the unknown concentration is directly proportional to the difference intitrant volumes.

There are known devices which can dispense precise measured amounts ofliquids quickly and easily. One such device includes a hollow cylinderwhich contains a supply of a solution to be dispensed. A plunger orpiston is selectively advanced within the cylinder bore by a micrometerscrew to force the solution out of the required titrant volume toequilibrate cylinder through a small orifice. By this device a liquidtitrant can be accurately dispensed or dosed in fine droplets. However,even with the use of such a device it is still necessary to manuallyrefill it with titrant after use, reset any readout apparatus, and, ofcourse, calculate the concentration of unknown sample.

Certain other known apparatus have appliedservo techniques for end pointdetection in titrations. And in still other known apparatus, such asthat disclosed in U. S. Pat. No. 3,143,393, Apparatus for AutomaticallyPerforming Chemical Operations and Similar or Related Operations by DeSeguin des Hons, a photocell monitors liquid level in a pipette andpositions a potentiometer to provide an analog signal indicative ofamounts of liquid transferred by the system.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore a primary objectand aim of this invention to provide method and apparatus forselectively dispensing liquids in discrete amounts and producing anelectric signal representative of the quantity of liquid dispensed.

Another object of the invention is to provide method and apparatus forselectively dispensing liquids in discrete amounts and producing anelectric signal selectively modifiable to represent the quantitydispensed of a constituent of said liquid.

A further object of the invention is the provision of method andapparatus for titrating a liquid sample and producing a selectivelymodifiable electric signal representative of the concentration of aconstituent of the sample.

Another object of the invention is to provide method and apparatus forthe dispensing of a liquid in discrete amounts and producing an electricsignal selectively modifiable to represent the difference between adispensed reference amount and any given subsequently dispensed amount.

A further object of the invention is to provide method and apparatus fordispensing a liquid in discrete amounts and producing an electric signalcorresponding to the difference in quantity of a common constituent of adispensed reference amount and that of any given subsequently dispensedamount.

A still further object of the invention is the provision of method andapparatus for back-titration of a liquid sample and production of anelectric signal selectively modifiable to represent the concentration ofa constituent of the sample.

Another object of the invention is to provide method and apparatus fordispensing liquids from a reservoir in which quantity dispensingmonitoring means are automatically reset during refill.

Yet another object is the provision of method and apparatus as in theabove described objects in which successive dispensing can beaccomplished semi-automatically and with readout means therefor notrequiring resetting and recalibration.

A further object is the provision of such method and apparatus in whichrepetitive dispensing is semi-automatically accomplished and readout oftitration results is automatic.

Still another object is the provision of titratio method and apparatusin which successive dispensing for back-titration are accomplishedsemi-automatically and backtitration results are provided in directautomatic readout.

Another object of the invention is the provision of method and apparatusas in the above described objects in which signal representation can beselectively changed without recalibration of apparatus.

In accordance with thepractice of this invention, means are provided fordosing from a titrant reservoir and transferring or metering discretequantities of the titrant to an unknown sample. Electric signalgenerating means are linked to the liquid transferring means forproviding an analog signal representative of the amount of liquidtransferred. Calibration circuits and means for weighting the generatedsignal to reflect titrant concentration and sample volume permit ob--taining direct readout on a display means, such as a digital voltmeterfor example, of a titrated sample concentration.

The calibration circuits and means also furnish analog subtraction ofthe generated signal establishing direct readout of the concentration ofa back-titrated sample.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of theapparatus of the invention illustrating its major components.

FIG. 2 is an elevational, partially sectional, view of DESCRIPTION OF APREFERRED EMBODIMENT Reference vis now made to FIG. 1 and the majoraspects of the invention which comprise generally a dispensing andelectric signal generating means 10 for transferring precise meteredamounts of titrant from a supply 11 along tubing 12 and 13 to be addedto an unknown sample in a mixing receptacle 14 carried by a suitablesupport 15 and producing an electric analog signal representative of theamount of liquid transferred. Monitoring and computing apparatus,identified generally as at 15', are related to the unit 10 via cablingl6 and receive energizing power via a further cable 17. Visualdisplay ofthe liquid volume transferred, the

quantity of a liquid constituent transferred, or the con-.

stituent concentration of a titrated or back-titrated sample, as thecase may be is provided at 18.

Generally as to operation, the entire system is primed with liquid(titrant) so that tubing 12, 13 and associated metering means to bedescribed are filled with the respective liquid. This is accomplished byreciprocally rotating control 19 to the limits of its clockwise andcounter clockwise travel, which serves to dose liquid or titrant fromthe reservoir 11 and prime the entire system. Control 19 then isreturned to its threshold position corresponding to that providingmaximum internal capacity of the liquid pumping means to be described,after which, with selector switch 20 in its lower position, the zerooffset potentiometer control 23 is adjusted for zero readout of 18,after which switch 20 is transferred to its upper reference position andzero offset control 22 is similarly adjusted for zero readout. Next anexact reference volume of liquid or titrant is dispensed by anappropriate increment of clockwise rotation of control 19, whichreference volume is measured otherwise than by the instrument andequipment of this invention. Without again moving control 19, referenceslope adjust potentiometer control 21 is adjusted so that the value ofthe above measured volume is displayedat 18. The instrument is nowcalibrated to display liquid aliquots dispensed in units of volume (Vt)at the means 18, when the selector switch is in upper or referenceposition.

With control 19 in the same position as above, and selector switch 20transferred to the lower or compute position, the instrument may now beoptionally calibrated to: (1) determine the quantity of dispensed liquidconstituent by adjusting a slope adjust control 24.

so that the value of the expression Ct X Vt is displayed, where Vt isthe volume of the previously dispensed reference aliquot and Ct is theconcentration of the liquid constituent; or (2) measure directly theconcentration of a titrated sample constituent by adjusting slopecontrol 24 such that the value of the expression ct/Vs X Vt, isdisplayed at 18, where Vt is the volume of the previously dispensedreference aliquot, Ct is the concentration of the titrant and Vs is thevolume of each sample to be subsequently titrated.

An alternate method of calibrating the instrument to automatically meterthe concentration of a titrated sample is by: (l) filling the instrumentwith titrant as previously described; (2) returning control 19 to itsthreshold position, and with the selector switch 20 in its lower orcompute position adjusting the zero offset control 23 so that thedisplay means 18 registers 0.000; (3) titrating a reference sample ofknown concentration and equal in volume to that of individual samples tobe subsequently titrated; and (4) with control 19 in the same positionas that reached at the end point of titration of the reference sample,adjusting slope adjust control 24 whereby the value of Cr, which is theconcentration of the titrated reference solution is displayed.

The apparatus may also be calibrated to compute and display units ofconcentration of a back-titrated sample by: (l) filling the instrumentwith titrant as previously described; (2) rotating control 19 to titratea reference solution aliquot of known concentration and equal in volumeto that to which each unknown sample is to be added for back titration;(3) with control 19 in the same position as that reached at the endpoint of the above titration, and selector switch 20 in its lower orcompute position, adjusting zero offset control until means 18 registers0.000, and (4) returning control 19 to threshold position and finallyadjusting slope adjust control 24 so that the means 18 registers thevalue (Vr X Cr)/Vs, where Vr is the volume of the reference solutiontitrated, Cr is the concentration of the titrated reference solution andVs is the volume of sample to be added subsequently to respective volumeVr of reference solution and back titrated. If at first theconcentration of the reference solution is unknown, this value may bedetermined by initially calibrating the instrument to function in itstitrimetric mode and titrating the reference solution with a titrant ofknown concentration. When the above calibration procedures forback-titration are accomplished, and when an appropriate volume ofsample is added to an appropriate volume of reference solution and themixture titrated, the instrument will automatically display theconcentration of the unknown added sample at the completion of thetitration.

The'description in the immediately preceding paragraphs of uses of theapparatus depicted in FIG. 1 has been confined to the manipulative stepswith the functional operation being provided hereinbelow in the detaileddescription of the associated mechanical and electrical apparatus.

FIG. 2 depicts a preferred form of liquid metering or pumping means foruse in the invention, comprising a generally T-shaped hollow chamber 26,the arms of which are connected to the tubing 12' and 13, respectively.Each chamber arm includes a pair of constricted portions 27, 28 and 29,30 for locating valving spheres 31 and 32, respectively.

The chamber 26 further includes a cylindrical portion 33 fixedly mountedby a hollow support 34 on the unthreaded sleeve extension 35 of aprecision threaded nut 36. Received within the nut 36 is a similarlyprecision threaded screw 37, an unthreaded extension 38 of which isreceived within the sleeve extension 35, and is I tandemly connected bymeans of a rotatable coupling 39 to a plunger 40 slidable within thebore of the cylindrical portion 33 of chamber 26. The nut 36 istranslatable within the bore of a collar housing 41 which nut is fixedagainst rotation therein by a longitudinal rib (not shown) projectingfrom the internal surface of 41 and received within a correspondinglongitudinal groove (not shown) on the external surface of the nut 36.Collar housing 41 is fixedly mounted to a chassis 42 by means of asupport 43. The head 44 of the precision threaded screw 37 is affixed toan adjustment shaft 45. It will be understood that equal increments ofrotation of shaft 45 result in equal translatory movements of thechamber 26 and its cylindrical extension 33 relative to the plunger 40,and that an adjustment of shaft 45 on rotation serves to advance orrecede, as the case may be, support 43, chamber 26 and extension 33 withrespect to screw extension 38 and plunger 40, to increase or decreasethe volume of liquid contained within the chamber 26.

The orifices 27 and 29 are so dimensioned that the valving spheres whenengaging the orifice walls prevent fluid flow. On the other hand,orifices 28 and 30 are of such geometry as to prevent the associatedsphere from passing, while allowing fluid to pass. That is, when thecylinder or barrel 33 is moved to the left as shown in FIG. 2, titrantis forced past the sphere 32, and through orifice 30 into output line13, whereas the valving sphere 31 is closed in orifice 27 and fluidcannot flow back into line 12. When the barrel moves to the right, thereverse valving condition exists, filling the cylinder 33 with titrantand preventing titrant flow to output line 13.

As shown in FIGS. 1 and 3, the shaft 45 is common to the shaft forpositioning the adjustable contact or slidewire of a potentiometer 46,which shaft is adjustably positioned by control knob 19 tosimultaneously transfer titrant and reset the adjustable contact on thepotentiometer resistance to reflect electrically such transfer.

Turning now to the circuit aspects of the invention as depicted in FIG.3, the potentiometer 46 includes a linear resistance 47 and adjustableslide contact 48, the latter being simultaneously adjusted by control 19with the dispensing or dosing movement of screw 37, support 43 andchamber 26.

Accordingly, the potential level presented to one side of a digitalvoltmeter 49 via lead 50 is dependent upon the position of the slidewire48. A zero offset potentiometer 51 includes a resistance 52 withadjustable slide contact 53 positioned by control knob 23. One end ofthe resistance 52 is connected to the slide contact 54 of a calibrationslope adjust potentiometer 55, the resistance of which is identified asat 56. The other end of the resistance 52 is tied to one end ofresistance 56. The calibration potentiometer is adjusted by control 24.

A potentiometer 57 including a resistance 58 and an adjustable contact59 and identified further as the reference slope adjust is adjusted bythe control 21. The potentiometer 60 including resistance 61 withadjustable contact 62 positioned by reference zero offset control 22 hasits resistance shunted across contact 59 and one end of resistance 58.

A selector switch assembly 63 includes three separate single-pole,double-throw switches 64, 65 and 66, operated in tandem by the switcharm 20. The selector switch assembly may optionally be a triplepole,double-throw arrangement.

One end of the linear taper potentiometer resistance 47 is connected tothe translatable pole of switch 66 by lead'67, and its other endinterconnects with the plus terminal of the D. C. voltage supply and thetranslatable pole of switch 64 via lead 68. The sliding contact 48 ofthe potentiometer 46 is connected to one input of the digital voltmeter49 via lead 50. The zero offset potentiometer sliding contact 53interconnects with the reference zero offset contact 62 and theremaining input of the digital voltmeter via lead 69. One end ofresistance 52 connects with an end of resistance 56, the common of whichis also related to the lower fixed pole of switch 64 by lead 70. Theother end of resistance 56 is connected to the lower fixed pole ofswitch 65 via lead 71. The sliding contact 54 connects with theremaining end of resistance 52, which common connection is also relatedto the lower fixed pole of switch 66 via lead 72. The upper fixed poleof switch 64 is connected to the common terminal of resistances 58 and61 by lead 73. The translatable pole of switch 65 is tied to the D. C.source negative terminal by lead 74, while the upper fixed pole of thissame switch connects with the free end of resistance 58 by lead 75. Theremaining end of resistance 61 is connected to the sliding contact 59and thence to the upper fixed pole of switch 66 by lead 76.

Circuit Operation for Liquid Dispensing and Titrimetry With the selectorswitch moved to its lowermost connective aspect, the commoned end ofresistance 56 is connected through lead 70 and switch 64 to the positivevoltage source terminal, whereas the other end of this same resistanceconnects through switch 65 to the negative voltage source terminal.Resistance 52 of zero offset potentiometer 51 shunts the commoned end ofresistance 56 and the slide contact 54, and, similarly, resistance 47via switch points 66 shunts the same portion of resistance 56.Accordingly, in the described connective mode, the two legs of thepotentiometers 46 and 51 form a Wheatstone bridge with the voltmeter 49arranged to indicate the degree of bridge imbalance.

The volume of liquid or titrant dispensed is linearly related to therotational movement of control 19 as is the value of the resistancetapped off 47 by sliding contact 48.

Consequently, if the sliding contact 53 is initially adjusted by meansof control 23 to null the bridge (zeroing the readout of the voltmeter49) at a point corresponding to the threshold position of control 19 andcontact 48, subsequent adjustment of control 19 simultaneously dispensestitrant and positions the slide contact 48 to produce an unbalance ofthe bridge and a resultant voltage potential read by the voltmeter whichis proportional to the volume of titrant dispensed.

The voltageapplied to the bridge determined by the position of theselectively adjustable contact 54 of the potentiometer 55 is aselectively variable analog multiplier of the bridge output.Accordingly, the potentiometer 55 functions as a slope adjust of thereadout, i.e., slope of the linear output.

More particularly, adjustment ofv calibrating potentiometer 55calibrates the readout to the voltmeter to display the value of anyvariable quantity which is a linear function of the volume of titrantdispensed. Accordingly, the readout to the voltmeter may be calibratedto register the value of any of the following quantities: (l) V, thevolume of liquid or titrant dispensed; (2) Ct V, the amount of liquidconstituent dispensed, where Ct is the concentration of the constituentin the dispensed liquid; (3) Ct/Vs X V, the concentration of a titratedsample at the end point of a titrant dispensing procedure, where C2 isthe concentration of the titrant and Vs is the volume of the titratedsample.

It will be understood by those skilled in the art that the calibratingpotentiometer 55 may alternatively be interfaced between the Wheatstonebridge and the voltmeter, or that a variable resistance may beincorporated within the voltmeter to achieve the same calibratingfunction without departing from the underlying spirit of the invention.

Back Titrimetry Adjustment of control 23 of zero offset potentiometer 51to null the bridge andzero the readout of the voltmeter 49 at that pointin the travel of control 19 previously reached at the end point of thetitration of the reference sample, sets and references the slidingcontact 53 to ratio at 52 a resistance which is equal to that tapped offthe resistance 47 by the contact 48 and which is therefore linear withthe volume of titrant required to titrate the reference sample to theend point. When control 19 is subsequently manipulated to refill thetitrant reservoir and to dispense the volume'of titrant sufficient totitrate to end point a combined sample containing a volume of sampleunknown added to a volume of reference sample equal to that employed inthe first or referencing titration, the slide contact 48 is reset and aresistance is tapped off the resistance 47 which is linearly related tothe volume of titrant required to titrate to end point the combinedreference and unknown sample. The potential difference now existingbetween the sliding contacts 48 and 53 is proportional to the differencein the volume of titrant required to titrate the reference sample, andthat volume of titrant required to titrate a combined aliquot ofreference sample and unknown sample.

A subsequent appropriate adjustment of the potentiometer 55 calibratesreadout to the voltmeter to register in appropriate units the 'value ofany selective quantity which is a linear function of the volumedifference and expressable by the equation f(V V )=k (V -V where V V isthe volume difference of the two aforementioned titrations and k is aconstant. Referring again to the equation employed in calculating backtitrimetric results, Cs Ct/Vs (V -V since the value Ct/Vs is a constantduring a back titrimetric procedure, it follows that the readout iscalibratable to register the value Cs, the concentration of the unknownsample at the end point of a back titrimetric procedure.

Memory Reference Circuit The reference slope adjust potentiometer 57 andthe reference zero adjust potentiometer 60 form a memory referencecircuit which duplicates the principal circuit already describedconsisting of calibrating potentiometer 55 and zero offset potentiometer51. Transferring the selector switch 63 to its upper position by thetoggle 20 electrically substitutes the potentiometers 57 and 60 for thepotentiometers 51 and 55. Accordingly, by means of this referencecircuit, the apparatus may be made to selectively register any one of apair of liquid characteristics.

Alternate Embodiment FIG. 4 illustrates a modified form of the inventionwhich is especially advantageous for handling titrants under hydrostaticpressure. For example, in the previously described apparatus if thetitrant container or reservoir were elevated above the general plane ofthe other equipment, siphon flow of titrant through the equipment couldbe produced without concomitant adjustment of the control 19, resultingin erroneous readout.

It is to be noted that the major part of the electrical circuitspertaining to computing and dispensing depicted in FIG. 4 are the sameas in FIG. 3, and where identical the same reference numeralshave beenused. In place of the ball check valves, this embodiment utilizessolenoid valves 77 and 78 which are normally closed in the unergizedstate. A slip clutch 79 driven by the shaft 45 actuates a switch 80during dispensing rotation thereof to open valve 78 and permitdispensing of titrant. However, as soon as the shaft 45 reverses, switch80 returns to the position shown in FIG. 4, closing 78 and opening 77.

What is claimed is: I

1. Apparatus for transferring liquid titrant from a reservoir to anoutlet and indicating liquid quantity transferred, comprising:

conduiting means interconnecting the reservoir and outlet;

pumping means interconnected with said conduiting means including a bodymember with a cavity interconnected with said conduiting means, pistonmeans disposed within said cavity, and an actuator providing relativetranslatory movement between the body member and piston means whenrotated in a first direction to move titrant from the reservoir, andwhen rotated in the second direction to move liquid to the outlet;

electric signal generating means including a resistance potentiometerhaving a slide contact that is secured to said pumping means actuatorwhereby said slide contact is adjustably positioned on rotation of saidactuator for adjusting the electric signal magnitude as a function ofactuator rotative movement; and

electric signal readout means connected to the signal generating meansfor providing an indication of liquid amount transferred.

2. Apparatus for transferring a liquid titrant from a reservoir to anoutlet and indicating the quantity of titrant transferred, comprising:

conduiting means interconnecting the reservoir with the outlet;

pumping means interconnected with said conduiting means including a bodymember with a cavity in fluid communicating relation with saidconduiting means, piston means disposed within said cavity, and anelongated rodlike actuator providing relative translatory movementbetween the body member and piston when rotated axially about its longdimension in a first direction to move titrant from the reservoir, andwhen rotated in the second direction to move liquid to the outlet;

electric signal generating means including a resistance potentiometerhaving a slide contact secured to said rodlike actuator, which slidecontact is adjustably positioned on rotation of said actuator to providean electric signal of magnitude functionally related to titranttransferred by said pumping means; and

means responsive to said electric signal for providing a digital displayof units of titrant transferred by said pumping means.

3. Apparatus for transferring liquid from a reservoir to an outlet andproviding an indication of liquid quantity transferred, comprising:

liquid conduiting means interconnecting the reservoir and outlet;

pumping means interconnected with the liquid conduiting means, saidpumping means including a piston received within a cylinder and threadeddrive means rotation of which in a first direction effects relativetranslation of the piston within the cylinder to transfer liquid towardsaid outlet from the reservoir;

electric signal generating means including a resistance potentiometerwith a slide contact integrally connected with said threaded drive meansand ad justably positioned on rotation of said drive means;

first and second electric circuit means of individually selectivelyadjustable impedance; switch means selectively actuable to interconnectthe potentiometer with the first or second circuit means in a Wheatstonebridge varying the electric signal magnitude per unit of elementmovement in accordance with the adjustment and connection of saidcircuit means; and readout means connected to the signal generatingmeans for providing readout indication of liquid amount transferred. 4.Apparatus as in claim 3, in which there are further provided firstvalving means located in the conduiting means between the pumping meansand reservoir second valving means in the conduiting means locatedbetween the pumping means and the outlet, and means for actuating thefirst and second valving means to opposite states for providingunidirectional liquid transfer.

5. Apparatus as in claim 3, in which said first and second electriccircuit means are adjustable to a relative impedance that said readoutmeans provides a direct indication of the concentration of a componentmaterial of said liquid transferred.

6. Apparatus for transferring a liquid from a reservoir to an outlet andindicating liquid quantity transferred, comprising:

conduiting means interconnecting the reservoir and outlet;

electrical signal generating means including a resistance potentiometerwith adjustable slide contact;

pumping means interconnected with both said conduiting means and saidelectrical signal generating means, said pumping means including:

a body member with a cavity in fluid communicating relation with saidconduiting means, piston means within the cavity, and actuator means forproviding relative translatory movement between the body member and thepiston means, said actuator means also being connected to thepotentiometer slide contact for positioning said slide contact when theactuator is moved in a first direction to move titrant from thereservoir and to adjust the electrical signal output to an initialpredetermined value, and when moved in a second direction to transfertitrant to the outlet and to adjust the electrical signal correspondingto the relative translatory motion of the body member and piston means;and

electrical signal readout means connected to the electrical signalgenerating means for providing an indication of liquid amounttransferred.

1. Apparatus for transferring liquid titrant from a reservoir to anoutlet and indicating liquid quantity transferred, comprising:conduiting means interconnecting the reservoir and outlet; pumping meansinterconnected with said conduiting means including a body member with acavity interconnected with said conduiting means, piston means disposedwithin said cavity, and an actuator providing relative translatorymovement between the body member and piston means when rotated in afirst direction to move titrant from the reservoir, and when rotated inthe second direction to move liquid to the outlet; electric signalgenerating means including a resistance potentiometer having a slidecontact that is secured to said pumping means actuator whereby saidslide contact is adjustably positioned on rotation of said actuator foradjusting the electric signal magnitude as a function of actuatorrotative movement; and electric signal readout means conNected to thesignal generating means for providing an indication of liquid amounttransferred.
 2. Apparatus for transferring a liquid titrant from areservoir to an outlet and indicating the quantity of titranttransferred, comprising: conduiting means interconnecting the reservoirwith the outlet; pumping means interconnected with said conduiting meansincluding a body member with a cavity in fluid communicating relationwith said conduiting means, piston means disposed within said cavity,and an elongated rodlike actuator providing relative translatorymovement between the body member and piston when rotated axially aboutits long dimension in a first direction to move titrant from thereservoir, and when rotated in the second direction to move liquid tothe outlet; electric signal generating means including a resistancepotentiometer having a slide contact secured to said rodlike actuator,which slide contact is adjustably positioned on rotation of saidactuator to provide an electric signal of magnitude functionally relatedto titrant transferred by said pumping means; and means responsive tosaid electric signal for providing a digital display of units of titranttransferred by said pumping means.
 3. Apparatus for transferring liquidfrom a reservoir to an outlet and providing an indication of liquidquantity transferred, comprising: liquid conduiting meansinterconnecting the reservoir and outlet; pumping means interconnectedwith the liquid conduiting means, said pumping means including a pistonreceived within a cylinder and threaded drive means rotation of which ina first direction effects relative translation of the piston within thecylinder to transfer liquid toward said outlet from the reservoir;electric signal generating means including a resistance potentiometerwith a slide contact integrally connected with said threaded drive meansand adjustably positioned on rotation of said drive means; first andsecond electric circuit means of individually selectively adjustableimpedance; switch means selectively actuable to interconnect thepotentiometer with the first or second circuit means in a Wheatstonebridge varying the electric signal magnitude per unit of elementmovement in accordance with the adjustment and connection of saidcircuit means; and readout means connected to the signal generatingmeans for providing readout indication of liquid amount transferred. 4.Apparatus as in claim 3, in which there are further provided firstvalving means located in the conduiting means between the pumping meansand reservoir, second valving means in the conduiting means locatedbetween the pumping means and the outlet, and means for actuating thefirst and second valving means to opposite states for providingunidirectional liquid transfer.
 5. Apparatus as in claim 3, in whichsaid first and second electric circuit means are adjustable to arelative impedance that said readout means provides a direct indicationof the concentration of a component material of said liquid transferred.